The invention relates to a portable appliance for detecting explosive materials, having an apparatus for generating and measuring emission of an indicator.
By way of example, the emission can be produced by excitation with radiation (fluorescence, phosphorescence) or by a chemical reaction (chemiluminescence). The focus is on the generation and measurement of the emission of indicator substances that are applied to a carrier. By way of example, a carrier can be a glass or a plastic on which the indicator substances (one or more) are applied as a thin layer. By way of example, indicator substances can be fluorescence-capable polymer molecules, the fluorescence of which changes after contacting certain analytes. Analytes are compounds, materials or substances about which a statement should be made within the scope of a measurement. The change in the fluorescence of the indicator substance is a clue about the existence of the analyte, or else a measure of the concentration thereof. The system with carrier and indicator substance is referred to as indicator below.
Apparatuses of this type have been known for a relatively long time and they are used, for example, in the field of detecting analytes such as explosive materials and other substances (drugs, toxic gases, and more) that are relevant to health and the environment. The indicator is contacted under defined conditions with the medium to be examined, the latter possibly being gaseous, for example. If explosive materials, for example, are situated in the medium, they are able to change the emission of the indicator.
WO 03/031953 presents an optical unit in which an indicator substance is situated as a layer on the radiation source for exciting the emission. Here, the radiation source is a GaN-LED. This emission reaches a detector via an optical filter, said detector capturing the emission in the forward direction.
U.S. Pat. No. 8,287,811 B1 presents an optical unit that contains an indicator with two indicator substances on a common carrier. The two indicator substances are applied to the two opposite sides of the carrier. Both indicator substances are irradiated with the same wavelength in the UV range. Quenching occurs if the one indicator substance is contacted by the analyte. The fluorescence of the other indicator substance is used as a reference signal. The fluorescences are steered in the direction of a lens onto a photomultiplier. A filter wheel with three filters is arranged in front of the photomultiplier.
U.S. Pat. No. 8,323,576 B2 describes an appliance system, the core of which is a cylindrical solid which may consist of glass, for example. This body is embodied as a capillary and heatable in a defined fashion. The capillary is divided into two. The first part serves as a gas inlet and as an adsorption and desorption section for the analytes to be detected. A second part contains an optical unit with an indicator substance applied to the inner wall. The indicator is impinged upon by a radiation source via a wavelength-selective filter. The measurement of the emission is carried out as a transmitted light measurement via the filter and receiver.
WO 2012/134436 A1 describes an indicator which likewise is embodied as a capillary and a common carrier for a plurality of indicator substances. In addition to the fluorescence, phosphorescence and chemiluminescence also come into question as emission signals. In one example, the capillary contains two indicator substances, which are each irradiated by a 405 nm LED. The measurement of the emission is carried out via filters and receivers. Here, the indicator itself serves as an optical waveguide.
WO 01/86263 A2 proposes an apparatus in which the excitation radiation of the radiation source is coupled into an optical waveguide, embodied as a splitter, via a filter and guided to the optical waveguide end face. A polymer that ensures an accumulation of the analyte is applied to this end face. Some of the emission is returned to the splitter by the same optical waveguide and steered onto a detector with a filter. The apparatus allows a plurality of such optical waveguide arrangements to be received. Hence, the overall system may have different excitation sources, filters, polymers and detectors.
In US 2014/0065720 A1, the fluorescence is produced by way of the surface plasmon-coupled emission (SPCE) method. The fluorescence is captured with a high signal-to-noise ratio, and so it can be measured with a high spectral resolution. For the purposes of carrying out the SPCE method, the indicator additionally contains a metal layer and a dielectric layer. The sensor is presented with a radiation source for excitation radiation.
In WO 2008/051189 A2, a fluorescence system is presented, said fluorescence system being equipped with filter wheels on both the excitation side and the emission side for the purposes of the spectral resolution. Many excitation and emission wavelengths are available using such a system.
The appliances should be suitable for detecting analytes such as explosive materials and other substances that are relevant to health and the environment. In part, they are equipped with great technical functionality and have a correspondingly complex structure. In another part, the appliances contain minimalized technical equipment.
It is an object of the invention to provide a fieldcapable, portable appliance having an apparatus for generating and measuring an emission for use in the detection of explosive materials, said appliance being well adapted to the application in harsh environments, being easily handled by an operator, having a relatively simple, robust structure and nevertheless being characterized by a high measuring certainty.
This object is achieved by a portable appliance in accordance with embodiments of the invention. Advantageous developments are set forth and claimed herein. The phrasing of all the claims is incorporated into the content of the description by reference.
On account of its structure, the portable appliance is suitable for detecting explosive materials by measuring optical emissions. To this end, use is made of appropriate indicators that react sensitively to these substances, the changes of said indicators being optically detectable by the presence of the searched-for analytes. Optionally, it is also possible to detect other substances that are relevant to health and the environment (such as, for example, drugs, toxic gases and more). To this end, use may possibly be made of other indicators. The apparatus for generating and measuring emission of an indicator is an essential functional constituent part of the appliance.
The apparatus for generating and measuring emission has a plurality of radiation sources, which can each emit quasi-monochromatic excitation radiation. In this application, the phrase “quasi-monochromatic excitation radiation” denotes excitation radiation from a relatively narrow wavelength range, for example with a spectral bandwidth of significantly less than 100 nm, wherein the spectral bandwidth may be of the order of approximately 10 nm or a few 10 nm, for example. The excitation radiation may also be referred to as “narrow bandwidth excitation radiation”. Then, the term “excitation wavelength” relates to a relatively narrow wavelength range. Consequently, the excitation radiation is not broadband white light, in particular. By way of example, light-emitting diodes (LEDs) or laser diodes can be used as radiation sources for producing the excitation radiation, or else broadband white light sources, the radiation of which is guided via at least one wavelength-selective device (e.g. a grating or a narrow bandwidth filter).
Consequently, the excitation is not performed using a continuous broadband spectrum (e.g. by means of white light), but in a single narrow bandwidth wavelength range or in a plurality of spectrally different, relatively narrow bandwidth wavelength ranges.
The radiation sources are arranged in a defined spatial arrangement with mutual spacing from one another. The spatial distribution of the radiation sources in the radiation area determines the location-dependent pattern of radiation sources, which can be used for the measurement.
The excitation light reaches the indicator area via an excitation beam path. To this end, the excitation beam path has at least one first imaging system. Then, emissions of the indicator substances can be produced at the locations at which the excitation radiation is imaged via the excitation beam path on the indicator area or onto the indicator area. Then, these locations form a pattern depending on the location in the indicator area. The pattern of these locations may correspond to the pattern of the radiation sources within the meaning of a geometric similarity, but this is not mandatory. A plurality of laterally distributed locations can be impinged upon by excitation radiation in the indicator area. The local distribution of the excitation radiation on the indicator area and the local distribution of the indicator substances are matched to one another.
An emission beam path serves to image the indicator area into a reception area in such a way that a pattern of emissions is producible in the reception area depending on the location. Thus, emissions can strike at different locations of the reception area. To this end, the emission beam path has at least one second imaging system. The pattern of emissions in the reception area may correspond to the pattern of locations of the indicator area, impinged upon by excitation radiation, within the meaning of a geometric similarity, but this is not mandatory.
If reference is made to an “imaging system” or an imaging optical unit within the scope of this application, this should mean that the imaging system can produce a magnified, reduced or a 1:1 image of an object without, in the process, modifying the form or the appearance of the object (apart from aberrations). The area or plane on which imaging takes place may, in the process, lie in an image plane of the imaging system or outside of the image plane.
A plurality of receivers are provided for receiving emissions from the reception area and for converting the received emissions into electrical signals. Here, a receiver is assigned to at most one indicator substance within the meaning of, at a given time, there not being two or more indicator substances that are assigned the same receiver. Consequently, at a given time, a receiver receives emission radiation from at most exactly one indicator substance assigned thereto. The emissions in the entrance area are locally decoupled from one another in such a way that the emissions are resolvable without mutual superposition of emissions. The emission received by a receiver can be assigned to exactly one of the indicator substances and one of the radiation sources. As a result of this, highly selective measurements with a high measurement accuracy are possible. A receiver can be optically adjusted in an ideal fashion to only the one indicator substance assigned thereto. As a result, ideal matching of the area (extent, form and size of the area) of the indicator substance to the active area of the receiver becomes possible. As result, it is possible to obtain a high signal-to-noise ratio (S/N ratio).
The appliance is designed as a portable appliance that can easily be carried and operated by a single person. In particular, the appliance can be constructed to be so small and light that it can be held in only one hand during use (hand-held appliance). Installation size and mass, and the robustness of the components installed therein, are optimized in view of this application. By way of example, the mass may be less than 2 kilograms, in particular less than 1.5 kilograms, but usually at least 0.5 kilograms. The installation size including the holding device for the indicator may be e.g. 50 cm or less, or 40 cm or less, or 30 cm or less (measured in the direction of greatest extent), with the installation size usually being at least 10 cm to 15 cm, however.
Even though, in principle, it is possible to arrange the excitation beam path and the emission beam path on different sides of the indicator area, provision is preferably made for the excitation beam path and the emission beam path to be arranged in a backward geometry such that the excitation beam path and the emission beam path are arranged on one and the same side of the indicator area or indicator. In this way, it is particularly easily possible to house the indicator in a holding apparatus that can be coupled to one side of the appliance and can easily be interchanged when required. The backward geometry may also be expedient in the case of a holding apparatus that is securely integrated into the appliance since, for example, all optical components can be housed on the same side of the indicator area.
The measurement geometry can be set by the structure in such a way that excitation radiation that has undergone specular reflection at the indicator, and hence radiation disturbing the emission measurement, does not strike the reception area to a relevant extent and hence is not able to reach a receiver either and increase the noise background there. In preferred embodiments, different angles of excitation radiation and emission radiation in relation to the surface normal of the indicator are provided in the region where the excitation radiation strikes for the purposes of avoiding or reducing the entrance into the emission beam path of intensity components of the excitation radiation that underwent specular reflection.
Preferably, this is achieved by virtue of optical axes of one or more or all imaging systems of the excitation beam path (first imaging system) and of the emission beam path (second imaging system) running obliquely in relation to one another in the region of the indicator area and not being arranged symmetrically in relation to the surface normal. By way of example, an angle between incident excitation radiation and emitted emission radiation may lie in the range from 20° to 60°, in particular in the range from 30° to 50°.
Preferably, no physical beam splitter (such as a dichroic mirror or a polarization beam splitter, for example) or geometric beam splitter (such as a mirror with at least one breach in the illuminated region, for example) is required for separating excitation beam path and emission beam path, and hence neither is provided either. This renders it possible to avoid typical problems that may arise when using beam splitters, for example stray light generated at the beam splitter.
The arrangement of excitation beam path and emission beam path may be such that optical axes of one or more or all imaging systems of the excitation beam path (first imaging system or first imaging systems) and one or more or all imaging systems of the emission beam path (second imaging system or second imaging systems) cross at a distance in front of the indicator area, and so points of intersection of the optical axes in the indicator area are laterally spaced apart. As a result, it is possible to ensure that excitation radiation, which undergoes specular reflection at one or more at least partly reflecting interfaces of the indicator (e.g. airindicator interface), practically cannot reach into the emission beam path and hence cannot reach the receivers. This contributes to being able to dispense with the use of excitation filters and/or emission filters, where applicable. The distance lies significantly outside of the manufacturing tolerances and may lie, for example, in the range from 1 mm to 10 mm, optionally also thereabove or therebelow.
Some embodiments are characterized by a wavelength-selective device with an entrance area and an exit area, wherein the entrance area can be impinged upon by the emission received in the reception area and the receivers are arranged in the exit area. As a result of this, it is possible to select certain narrower wavelength ranges from a broader emission spectrum, or choose these for the evaluation. The same wavelength range may be chosen for all receivers. It is also possible to choose different wavelength ranges that have a spectral distance from one another for different receivers. The wavelength-selective device may be interchangeable in order to be able to adapt the appliance in an ideal fashion to different measurement problems. However, a wavelength-selective device between the reception area and the receivers is not mandatory.
A separate receiver may be assigned to each indicator substance. Interstices without light-sensitive areas may lie between the receivers. The receivers may be individually adjustable or adjustable separately from one another such that each measurement channel can be set in an optimized fashion for its measurement problem. The number of receivers may correspond to the number of effectively employable excitation channels.
Preferably, provision is made for one or more radiation sources to be assigned to each indicator substance, wherein a radiation source is assigned to at most one indicator substance, and so there are not two or more indicator substances that are assigned the same radiation source. As a result, the radiation source can be optically adjusted in an ideal fashion to only the one indicator substance assigned thereto. As a result, an ideal matching of the area of the indicator substance to that of the radiation source is possible. This is conducive to obtaining a high signal-to-noise ratio.
In many embodiments, photomultipliers that have high sensitivities even in the case of low measurement-relevant intensities are used as receivers. In particular, it is possible to use semiconductor-based photomultipliers, e.g. Si-photomultipliers (Si-PMTs). These are mechanically robust, relatively insensitive to tremors and offer very high sensitivities in the case of relatively small sensitive areas. Alternatively, it is also possible to use e.g. conventional photomultipliers or photodiodes as receivers.
As mentioned, an imaging system can produce a magnified, reduced or a 1:1 image of an object without, in the process, modifying the form or the appearance of the object (apart from aberrations). The area or plane on which imaging takes place may, in the process, lie in an image plane of the imaging system or outside of the image plane. If reference is made to “non-imaging optics”, this should mean that the employed optical elements (one or more) act as beam shapers that can change the form or the appearance of an object. Imaging optics and non-imaging optics can be combined in an optical channel (excitation channel or emission channel).
It is possible to construct the apparatus in such a way that the excitation beam path only has a single excitation channel with a first imaging system, to which two or more radiation sources are then assigned. The excitation channel may provide a plurality of sub-channels for the excitation radiation propagating from the radiation sources to the indicator area, with a common optical axis.
By contrast, many embodiments are constructed in such a way that the excitation beam path has a plurality of excitation channels, i.e. two or more excitation channels, wherein each excitation channel has a first imaging system that defines an optical axis of the corresponding excitation channel. By way of example, the number of mutually separate excitation channels may lie in the range from two to ten, in particular in the range from three to six. Hence, the excitation radiation from different radiation sources can be guided to the indicator on separate excitation channels that are optically separated from one another. As a result, there is structural prevention of cross talk between the excitation channels.
In this application, the term “excitation channel” denotes an optical system having at least one optical element configured with refractive power, for example a lens, and optionally further optical elements, such as e.g. at least one beam shaper and/or at least one filter. An excitation channel guides radiation from one or more radiation sources into the indicator area in a defined manner.
The arrangement may be such that provision is made of exactly one excitation channel for each indicator region, and so the number of excitation channels corresponds to the number of indicator regions. The term “indicator region” denotes the location of the indicator substance or the region in which an indicator substance is situated. It is also possible to use an excitation channel for guiding excitation radiation to two or more indicator regions that are separate from one another.
Likewise, a plurality of mutually separate emission channels may be provided for the emission beam path.
By contrast, provision is made in one embodiment for the emission beam path to have a common imaging system (second imaging system) for all emissions, said imaging system defining an optical axis of the emission beam path. Thus, a single emission channel may suffice. It may provide a plurality of sub-channels for the emissions propagating from the indicator to the reception plane in the case of a common optical axis.
In one embodiment with a plurality of excitation channels, the excitation channels form a symmetric arrangement in relation to the emission channel. In particular, the arrangement may be mirror symmetric in relation to at least one symmetry plane that contains the optical axis of the emission beam path.
In an embodiment with a plurality of excitation channels, the excitation channels and the emission channel form a conical arrangement, wherein optical axes of the excitation channels are arranged on a lateral conical face that surrounds the emission channel and the optical axis of the emission channel is arranged along the axis of the cone. As a result of this, a plurality of radiation-guiding channels with very compact dimensions can be provided between the radiation sources, the indicator and the reception plane or the receivers. In preferred embodiments, the cone tip of the conical arrangement, i.e. the point of intersection of the optical axes of the excitation channels, does not lie in the indicator area but at a distance therefrom, in particular in front of the indicator area.
In some cases, it may be expedient for a beam shaper to be arranged in an excitation channel between a radiation source and the indicator plane. Here, in general, the term “beam shaper” denotes non-imaging optics which are able to change the form or the appearance of an object. By way of example, a beam shaper can have a diffuser function. By way of example, the beam shaper can have a microstructured component (e.g. a diffractive optical element) and/or it may be designed to convert a non-uniform intensity profile into a uniform and steep intensity profile. As a result of this, it is possible to obtain a uniform or homogeneous illumination of regions to be excited (spots) of the indicator substances, even if use is made of small, quasi-punctiform radiation sources with a non-uniform emission characteristic, as a result of which meaningful quantitative comparisons can be facilitated and the measurement accuracy can be increased.
In some embodiments, provision is made of a clock for actuating radiation sources, wherein the clock is configured in such a way that all radiation sources are clocked sequentially in series or that some of the radiation sources or all radiation sources are clocked simultaneously or that radiation sources are clocked alternately. As a result, the radiation sources can work in flash operation, and so they can be activated and deactivated in a temporally defined manner by way of a clock generator. These variants can be described in such a way that the radiation area does not only represent a pattern of radiation sources depending on location, but also a pattern depending on time. In this case, a pattern can always be present whenever at least one dependence (location, time) exists.
With the aid of a clock, it is also possible to produce a secondary or virtual radiation source in an excitation channel, said secondary or virtual radiation source being able to selectively emit different excitation wavelengths. In some embodiments, two or more radiation sources for emitting different excitation wavelengths are assigned to at least one of the excitation channels, wherein the radiation sources are alternately clockable by means of a clock and a radiation merging device is provided for selective input coupling of excitation radiation from the radiation sources into the excitation channel. By way of example, the radiation merging device can have a beam shaper in the form of a diffuser.
In some embodiments, a particularly compact and robust configuration is achieved by virtue of all optical elements of the apparatus, i.e. all optical elements of the excitation beam path and of the emission beam path, being installed or integrated into a single component. The component may serve as an optics holder for all optical elements. It may consist of a single piece (monolithic component) or else it may be securely assembled from two, three or more components. By way of example, such a component can be produced as an injection-molded part or else by sintering or by material-ablating processing from the whole. All components in the apparatus that are able to spatially, temporally and spectrally modify the properties of radiation are considered to be optical elements. Predominantly, these are the functions of imaging, steering and guiding, and of shaping the radiation. As a result of the combined housing of all optical elements in one and the same component that serves as an optics holder, the relative arrangement of the optical elements is continuously maintained, even in the case of relatively strong movements of the entire apparatus, in the case of jolts or tremors. Thus, the appliance can also be used in harsh environments; measurements with a high accuracy are possible even when an operator holds the appliance with one hand and the entire appliance is easily moved as a result thereof.
Preferably, a plurality of receiving channels for receiving the optical elements of at least one excitation channel and one emission channel are formed in the component. The receiving channels, which can be introduced into an initially solid component by way of drilling or electrical discharge machining, for example, may each have a rotationally symmetric form, for example; other cross-sectional shapes are likewise possible. Preferably, the optical elements are mounted individually or in groups in mounting elements, e.g. sleeve-shaped mounting elements, that fit into assigned portions of the receiving channels in the component and which can be inserted into the receiving channels and can be anchored there when assembling the apparatus.
An appliance that is specifically configured for detecting explosive materials preferably has an evaluation device, connected to the receivers, for receiving electrical signals of the receivers and for evaluating the spectral information about the emissions contained in the signals, wherein the evaluation device is configured in such a way that at least one of the following information items is establishable and can be output to an operator or user of the information: information items about the amount of one or more searched-for analytes; information about the type of one or more analytes.
Here, the analytes respectively comprise one or more explosive materials or groups of explosive materials. Information about spectral characteristics of fluorescence spectra and/or luminescence spectra of the target substances may be stored in the form of target substance data in a memory of the evaluation device, it being possible to resort to said data for comparison operations within the scope of the evaluation.
The invention also relates to the use of the appliance for detecting explosive materials, wherein use is made of an indicator that has at least one indicator substance which, in the case of irradiation by excitation radiation and contact with an analyte containing at least one explosive material, exhibits a reduction or increase in the fluorescence intensity emitted by the indicator substance.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.